Valter
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TFTP via VRF
How does Internet work - We know what is networking
As you can see from my article list, I’m going through some VRF configuration in the last few weeks I ran into this today and it sounded interesting enough to share it with you. The issue with TFTP IOS image copy to flash when having all interfaces in specific VRF and no interface in Global Routing Table. Long story short, you kick in this command for normal IOS download to the router: R1#copy tftp://10.10.10.11/c890-universalk9-mz.154-3.M5.bin flash: Destination filename ? Accessing tftp://10.10.10.11/c890-universalk9-mz.154-3.M5.bin... %Error opening tftp://10.10.10.11/c890-universalk9-mz.154-3.M5.bin (Timed out) …and it isn’t working of course. The issue is in having all interfaces member of
VRF – Virtual Routing and Forwarding
How does Internet work - We know what is networking
Ever needed one extra router? It’s possible to split the router into more logical routers by using VRF. How? Here’s how! Virtual Routing and Forwarding or VRF allows a router to run more that one routing table simultaneously. When running more routing tables in the same time, they are completely independent. For example, you could use same or overlapping IP addresses in both VRFs and it can be used without conflict. It is possible to use same VRF instance on more routers and connect every instance separately using VRF dedicated router port or only a sub-interface. You can find VRFs to be used
Static Route Load Balance
How does Internet work - We know what is networking
Routing table will then leave to the switching process the job of load-sharing. That is, route-cache mechanisms like CEF on Cisco device will do load-share per session using source-destination IP.
What is route recursion
How does Internet work - We know what is networking
We are going back to networking basics with this post. In few lines below you will find most important theory that makes network gear do its job. The main router job is to making routing decisions to be able to route packets toward their destination. Sometimes that includes recursive lookup of routing table if the next-hop value is not available via connected interface. Routing decision on end device like PC, Tablet or Phone If one device wants to send a packet to another device, it first needs to find an answer to these questions: Is maybe the destination IP address chunk of local subnet
Control Plane Protection in Cisco IOS
How does Internet work - We know what is networking
CoPP – Control Plane Protection or better Control Plain Policing is the only option to make some sort of flood protection or QoS for traffic going to control plane. In the router normal operation the most important traffic is control plain traffic. Control plane traffic is traffic originated on router itself by protocol services running on it and destined to other router device on the network. In order to run properly, routers need to speak with each other. They speak with each other by rules defined in protocols and protocols are run in shape of router services. Examples for this
How Encryption of Network Traffic Works?
How does Internet work - We know what is networking
I recently started studying again, this time as an attempt of deep-diving into some security concepts for one of my PhD courses. It’s interesting how, as much as you try to escape from it, mathematics will sooner or later catch you somewhere and you will need to learn a bit more of it. At least that happened to me… In this process I realised that if you go beyond simple security theory and network device configuration all other stuff is pure mathematics. The reason behind my unplanned course in mathematics is explained through the rest of this text. It will
Nagle’s algorithm
How does Internet work - We know what is networking
This article it’s not about mathematics, don’t be afraid. I’m running a networking blog and it’s not my intention to speak or write about anything related to mathematics. Biggest math problem that I’ve done in last few years is some simple subneting, EIGRP metric calculation and that is where I stopped with math for now. On the other hand I love the theory behind algorithms, specially if the algorithm is used in networking and if it is so simple and powerful as Nagle’s algorithm. You can guess, John Nagle is the name of the fellow who created the algorithm. He
Proxy ARP
How does Internet work - We know what is networking
I found differed kinds of explanations about what that Proxy ARP is all about. After going through all of them this explanation came out. It is fairly simple technique for nodes to get MAC address of a destination host that is on the same subnet but behind a router. It’s a technique that enables our R7 router on the image below to proxy ARP request from C1 computer which tries to find MAC address of computer C3. You need to note that C1 has address from /16 range and that is why it thinks that 192.168.50.50 is the same subnet as
Mitigate DoS Attack using TCP Intercept on Cisco Router
How does Internet work - We know what is networking
This is really cool feature on Cisco router not usually mentioned until you dig a little deeper inside Cisco IOS. But first a bit of theory… What is TCP SYN flood attack TCP 3-way handshake SYN flood DoS attack happens when many sources start to send a flood of TCP SYN packets usually with fake source IP. This attack uses TCP 3-way handshake to reserve all server available resources with fake SYN requests thus not allowing legitimate users to establish connection to the server. SYN packet is the first step in TCP 3-way handshake where client sends connection synchronization request
How to generate network packets – Ostinato Packet/Traffic Generator
How does Internet work - We know what is networking
Network Packet Generator or Network Traffic Generator is a tool every network engineer will sooner or later want to use. Here’s one I found and it’s great! First time I saw an Ethernet frame in details on my CCNA class back in 2010 I immediately got the idea about generating some packets on my own. It was logical next step to ask myself: “Ok, so how can I make one of those and see what happens when I send it out on the network?”. I was not really sure that there is a tool that would make it possible. Don’t get me wrong,
How to generate network packets – Ostinato Packet/Traffic Generator
SDN SOFTWARE DEFINED NETWORKS: AN OVERVIEW
How does Internet work - We know what is networking
Flowing text is a project done as a part of academic work that I am involved with for last few years at the University of Rijeka – Department of Informatics. It’s a short overview at latest achievements in the field of network automation with some lab experiments done to test different paths across the network. The work was presented at 6th International Conference on Information Technologies and Information Society (ITIS2014). The scope of ITIS events are the applications of IT, particularly in social sciences. The conference also covers a wider range of topics related to IT and computational modeling and
How to Enable Dot1x – more complex setup for wired network
How does Internet work - We know what is networking
This one is long. Do not be afraid though, I made it just to give you the fastest way to deploy functional dot1x to your company HQ without reading even more documentation and searching for those little timer default settings. I the article prior to this I showed you how to setup your environment with simple dot1x and make it as simple as possible. I will not repeat again the part about setting up Radius Clients on server side, everything else is here once again just more complex. Now is time for a more complex example that will make your implementation
How to Enable Dot1x authentication for wired clients
How does Internet work - We know what is networking
If your LAN is extending to some places where unauthorised people can just plug in and gain access to your protected network, it’s time to implement some security on your access switch. The best thing to do is to implement IEEE 802.1X port-based authentication which will enable users/machine authentication and prevent unauthorized devices from getting access switch port running when connected. IEEE 802.1X port-based authentication is mostly called simply as dot1x. In this article I will show you how to configure some basic dot1x stuff on switch side. I will also include Windows machine side of configuration as this is something most people presume
Why numbering should start at zero?
How does Internet work - We know what is networking
Please note: This has nothing to do with networking in particular! Not if you look from only one perspective. If you look from totally different perspective, with Cisco ACI and all other SDN solutions, you will probably meet with Python programming language (because you will) and then, somewhere in beginning of Python exploration this is the first question that will cross your mind. Of course, if you think like me! Although not directly related to networking, the question bothered me for some time now and the answer is not only really logical when you read it but it is also
Why numbering should start at zero?
How does Internet work - We know what is networking
Please note: This has nothing to do with networking in particular! Not if you look from only one perspective. If you look from totally different perspective, with Cisco ACI and all other SDN solutions, you will probably meet with Python programming language (because you will) and then, somewhere in beginning of Python exploration this is the first question that will cross your mind. Of course, if you think like me! Although not directly related to networking, the question bothered me for some time now and the answer is not only really logical when you read it but it is also
What is a non-blocking switch?
How does Internet work - We know what is networking
It is fairly common to hear about switch being non-blocking. It’s because almost all switches today are non-blocking. But what that means? When I asked people around me on what exactly non-blocking switch means, they were unable to get to the same conclusion. I was going through a lot of different internet places and vendor documents before I wrote this here, but, do not hesitate to add something in comments if you have different view on the subject. Line-rate switch means the same as if you would said wire-speed switch. It basically means that this switch has the forwarding capacity that supports concurrently
What is a non-blocking switch?
How does Internet work - We know what is networking
It is fairly common to hear about switch being non-blocking. It’s because almost all switches today are non-blocking. But what that means? When I asked people around me on what exactly non-blocking switch means, they were unable to get to the same conclusion. I was going through a lot of different internet places and vendor documents before I wrote this here, but, do not hesitate to add something in comments if you have different view on the subject. Line-rate switch means the same as if you would said wire-speed switch. It basically means that this switch has the forwarding capacity that supports concurrently
HOL Head-of-line blocking
How does Internet work - We know what is networking
Head-of-line blocking (HOL blocking) in networking is a performance issue that occurs when a bunch of packets is blocked by the first packet in line. It can happen specially in input buffered network switches where out-of-order delivery of packets can occur. A switch can be composed of input buffered ports, output buffered ports and switch fabric. When first-in first-out input buffers are used, only the first received packet is prepared to be forwarded. All packets received afterwards are not forwarded if the first one cannot be forwarded. That is basically what HOL blocking really is.If there’s no HOL blocking happening,
HOL Head-of-line blocking
How does Internet work - We know what is networking
Head-of-line blocking (HOL blocking) in networking is a performance issue that occurs when a bunch of packets is blocked by the first packet in line. It can happen specially in input buffered network switches where out-of-order delivery of packets can occur. A switch can be composed of input buffered ports, output buffered ports and switch fabric. When first-in first-out input buffers are used, only the first received packet is prepared to be forwarded. All packets received afterwards are not forwarded if the first one cannot be forwarded. That is basically what HOL blocking really is. If there’s no HOL blocking
TCAM and CAM memory usage inside networking devices
How does Internet work - We know what is networking
As this is networking blog I will focus mostly on the usage of CAM and TCAM memory in routers and switches. I will explain TCAM role in router prefix lookup process and switch mac address table lookup. However, when we talk about this specific topic, most of you will ask: how is this memory made from architectural aspect? How it is made in order to have the capability of making lookups faster than any other hardware or software solution? That is the reason for the second part of the article where I will try to explain in short how are the most usual